A. M. Gasparyan

Ruhr University Bochum

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E. Epelbaum

Ruhr University Bochum

H. Krebs

Ruhr University Bochum

C. Hanhart

Forschungszentrum Jülich

J. Haidenbauer

Forschungszentrum Jülich

J. Gegelia

Ruhr University Bochum

Matthias Lutz

GSI Helmholtz Centre for Heavy Ion Research

Ulf-G. Meißner

Forschungszentrum Jülich

J. Speth

Forschungszentrum Jülich

V. Baru

Ruhr University Bochum

Matthias R. Schindler

BMW Group (Germany)

Cooperative Institutions

Forschungszentrum Jülich

Joint Institute for Nuclear Research

Petersburg Nuclear Physics Institute

Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati

Campbell Collaboration

Thomas Jefferson National Accelerator Facility

Argonne National Laboratory

Istituto Nazionale di Fisica Nucleare

European Organization for Nuclear Research

University of Bonn

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Pion-nucleon scattering in a meson-exchange model

Physical Review C (2003)

A. M. Gasparyan J. Haidenbauer C. Hanhart J. Speth

The $\ensuremath{\pi}N$ interaction is studied within a meson-exchange model and in a coupled-channels approach which includes the channels $\ensuremath{\pi}N$, $\ensuremath{\eta}N$, as well as three effective $\ensuremath{\pi}\ensuremath{\pi}N$ channels, namely, $\ensuremath{\rho}N$, $\ensuremath{\pi}\ensuremath{\Delta}$, and $\ensuremath{\sigma}N$. Starting out from an earlier model of the J\"ulich group systematic improvements in the dynamics and in some technical aspects are introduced. With the new model an excellent quantitative reproduction of the $\ensuremath{\pi}N$ phase shifts and inelasticity parameters in the energy region up to $1.9\phantom{\rule{0.3em}{0ex}}\text{GeV}$ and for total angular momenta $J\ensuremath{\leqslant}3∕2$ is achieved. Simultaneously, good agreement with data for the total and differential $\ensuremath{\pi}N\ensuremath{\rightarrow}\ensuremath{\eta}N$ transition cross sections is obtained. The connection of the $\ensuremath{\pi}N$ dynamics in the ${S}_{11}$ partial wave with the reaction $\ensuremath{\pi}N\ensuremath{\rightarrow}\ensuremath{\eta}N$ is discussed.

Partial wave analysis

10.1103/physrevc.68.045207

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Citations (104)

Three-nucleon force in chiral effective field theory with explicit Δ (1232) degrees of freedom: Longest-range contributions at fourth order

Physical review. C (2018)

H. Krebs A. M. Gasparyan E. Epelbaum

We analyze the longest-range two-pion exchange contributions to the three-nucleon force at leading-loop order in the framework of heavy-baryon chiral effective field theory with explicit $\mathrm{\ensuremath{\Delta}}$(1232) degrees of freedom. All relevant low-energy constants which appear in the calculation are determined from pion-nucleon scattering. Comparing our results with the ones obtained in the $\mathrm{\ensuremath{\Delta}}$-less theory at next-to-next-to-next-to-next-to leading order (${\mathrm{N}}^{4}\mathrm{LO}$), we find effects of the $\mathrm{\ensuremath{\Delta}}$ isobar for this particular topology to be rather well represented in terms of resonance saturation of various low-energy constants in the $\mathrm{\ensuremath{\Delta}}$-less approach.

Effective field theory

10.1103/physrevc.98.014003

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Citations (30)

How to extract theΛNscattering length from production reactions

Physical Review C (2004)

A. M. Gasparyan J. Haidenbauer C. Hanhart J. Speth

A dispersion integral is derived that allows one to relate directly (spin dependent) $\Lambda N$ invariant mass spectra, measured in a large-momentum transfer reaction such as $pp\to K^+p\Lambda$ or $\gamma d\to K^+n\Lambda$, to the scattering length for elastic $\Lambda N$ scattering. The involved systematic uncertainties are estimated to be smaller than 0.3 fm. This estimate is confirmed by comparing results of the proposed formalism with those of microscopic model calculations. We also show, for the specific reaction $pp\to K^+\Lambda p$, how polarization observables can be used to separate the two spin states of the $\Lambda N$ system.

10.1103/physrevc.69.034006

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Citations (55)

Nucleon-nucleon interaction in chiral effective field theory with a finite cutoff: Explicit perturbative renormalization at next-to-leading order

Physical review. C (2022)

A. M. Gasparyan E. Epelbaum

We present a study of two-nucleon scattering in chiral effective field theory with a finite cutoff to next-to-leading order in the chiral expansion. In the proposed scheme, the contributions of the lowest-order interaction to the scattering amplitude are summed up to an arbitrary order, while the corrections beyond leading order are iterated only once. We consider a general form of the regulator for the leading-order potential including local and nonlocal structures. The main objective of the paper is to address formal aspects of renormalizability within the considered scheme. In particular, we provide a rigorous proof, valid to all orders in the iterations of the leading-order potential, that power-counting breaking terms originating from the integration regions with momenta of the order of the cutoff can be absorbed into the renormalization of the low energy constants of the leading contact interactions. We also demonstrate that the cutoff dependence of the scattering amplitude can be reduced by perturbatively subtracting the regulator artifacts at next-to-leading order. The obtained numerical results for phase shifts in $P$ and higher partial waves confirm the applicability of our scheme for nucleon-nucleon scattering.

Cut-off

Effective field theory

Iterated function

10.1103/physrevc.105.024001

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Citations (18)

A new approach to chiral two-nucleon dynamics

Proceedings of The 8th International Workshop on Chiral Dynamics — PoS(CD15) (2013)

A. M. Gasparyan Matthias Lutz E. Epelbaum

A novel scheme developed recently for analyzing pion-nucleon scattering using chiral Lagrangian is applied to the nucleon-nucleon interaction close to threshold.Partial-wave amplitudes are obtained by an analytic extrapolation of subthreshold reaction amplitudes computed in chiral perturbation theory, where the constraints set by analyticity and unitarity are used to stabilize the extrapolation.Phase shifts are analyzed up to laboratory energies T lab ≃ 250 MeV in terms of the parameters relevant at next-to-next-to-leading order.The convergence properties of the method are discussed.

Unitarity

Subthreshold conduction

10.22323/1.172.0089

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Spin observables in pion photoproduction from a unitary and causal effective field theory

arXiv (Cornell University) (2010)

A. M. Gasparyan Matthias Lutz

Pion photoproduction is analyzed with the chiral Lagrangian. Partial-wave amplitudes are obtained by an analytic extrapolation of subthreshold reaction amplitudes computed in chiral perturbation theory, where the constraints set by electromagnetic-gauge invariance, causality and unitarity are used to stabilize the extrapolation. The experimental data set is reproduced up to energies $\sqrt{s}\simeq 1300$ MeV in terms of the parameters relevant at order $Q^3$. We present and discuss predictions for various spin observables.

Unitarity

Effective field theory

Causality

Parity (physics)

Field theory (psychology)

10.48550/arxiv.1012.5948

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Citations (1)

Nucleon polarizabilities in covariant baryon chiral perturbation theory with explicit Δ degrees of freedom

Physical review. C (2021)

M. Thürmann E. Epelbaum A. M. Gasparyan H. Krebs

We compute various nucleon polarizabilities in chiral perturbation theory implementing the $\mathrm{\ensuremath{\Delta}}$-full ($\mathrm{\ensuremath{\Delta}}$-less) approach up to order ${\ensuremath{\epsilon}}^{3}+{q}^{4}$ (${q}^{4}$) in the small-scale (chiral) expansion. The calculation is carried out using the covariant formulation of $\ensuremath{\chi}\mathrm{PT}$ by utilizing the extended on-mass shell renormalization scheme. Except for the spin-independent dipole polarizabilities used to fix the values of certain low-energy constants, our results for the nucleon polarizabilities are pure predictions. We compare our calculations with available experimental data and other theoretical results. The importance of the explicit treatment of the $\mathrm{\ensuremath{\Delta}}$ degree of freedom in the effective field theory description of the nucleon polarizabilities is analyzed. We also study the convergence of the $1/m$ expansion and analyze the efficiency of the heavy-baryon approach for the nucleon polarizabilities.

Padé approximant

Effective field theory

10.1103/physrevc.103.035201

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Citations (6)

Two-nucleon scattering: Merging chiral effective field theory with dispersion relations

The European Physical Journal A (2013)

A. M. Gasparyan Matthias Lutz E. Epelbaum

Unitarity

Subthreshold conduction

Effective field theory

Dispersion relation

10.1140/epja/i2013-13115-7

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Citations (14)

Nuclear Forces for Precision Nuclear Physics: A Collection of Perspectives

Few-Body Systems (2022)

Ingo Tews Zohreh Davoudi A. Ekström J. D. Holt Kevin Becker

Nuclear data

Nuclear force

10.1007/s00601-022-01749-x

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Citations (31)

Explicit renormalization of the nucleon-nucleon interaction in chiral EFT and non-perturbative effects

Proceedings of The 8th International Workshop on Chiral Dynamics — PoS(CD15) (2024)

A. M. Gasparyan E. Epelbaum

Nucleon-nucleon interaction is studied within chiral effective field theory with a finite cutoff at next-to-leading order in the chiral expansion. The leading order interaction is resummed non-perturbatively, whereas the next-to-leading-order terms are taken into account in a perturbative manner. Explicit renormalizability of such a scheme is proven in certain important cases. In particular, it is verified whether the power-counting breaking terms originating from the integration regions characterized by large momenta can be absorbed by the renormalization of the low energy constants. The importance of non-perturbative effects is analyzed in detail.

Cut-off

Non-perturbative

Effective field theory

10.22323/1.413.0079

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